5.3L LS Small Block Build - LS Modern Mouse: Part 2

We try some more aggressive cams and nitrous on our 5.3 LS guinea pig.

Loyal readers of Super Chevy (you know who you are) will no doubt remember our first adventure with Modern Mouse last month, but here is a recap for those of you just joining the party. Back in part one, we plucked a 5.3L LM7 truck motor from a local wrecking yard and propped it up on the dyno. As with our previous SBC rodent series (Major Mouse, Danger Mouse), our plan was to subject Modern Mouse to all manner of modifications, ranging from the mild to wild, even venturing off into the bizarre.

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To get the party started, we simply installed the motor and managed a few simple bolt-ons, namely ported stock heads, a cam, and an intake. The combination of TEA CNC 5.3L heads, a mild Comp hydraulic roller cam, and the Fast LSXR intake netted us 445 hp and 443 lb-ft of torque (100 hp and 70 lb-ft over the baseline runs).

These were good numbers considering the mild cam profile (212/218 @ 0.050). Those of you wondering why we didnít start with a larger 5.7L, 6.0L, or even 6.2L should know that the 5.3L is more readily available and considerably less expensive than any of its big brothers. Affordability is a critical element, but fear not: increased displacement is definitely on the to-do list.

After a review of the hard parts currently employed on Modern Mouse, we came to one simple conclusion—the thing needs more camshaft. Back in part one, we chose the conservative route and installed a cam that offered sizable power gains without negatively affecting things like idle quality and (likely) fuel mileage. That gains were present through the entire rev range was a good sign, but the 5.3L was now sporting heads and an intake manifold that could support 600 hp. While we knew 600 hp was out of the question in normally aspirated trim, we also knew that we could get a lot closer to 500 hp with a simple cam change. If not the cam alone, then certainly with a few other tricks we had up our sleeve. The icing on the performance cake came in the form of a plate nitrous system from NOS. The wet system offered plenty of power, but in deference to our stock short-block we installed what might be considered conservative jetting. As luck would have it, we also had the perfect displacement test, having run a 4.8L for sister-pub Hot Rod magazine with identical components.

Part two of Modern Mouse begins where part one left off, with our 5.3L sporting CNC-ported stock heads from Total Engine Airflow, a Comp XR265HR cam and a FAST LSXR intake and throttle body. Also present were the American Racing headers, a Meziere electric water pump and a FAST XFI/XIM management system. Equipped as such, Modern Mouse managed peak numbers of 445 hp at 5,900 rpm and 434 lb-ft at 5,000 rpm. With plenty of head and intake flow, we decided to further improve the peak power numbers of 5.3L, even if the additional power came at the expense of low-speed torque production. If the 5.3L were to see some strip action, the additional power would certainly come in handy. If you are all about torque and driveability, stick with the smaller XR265HR grind, but for this installment, we replaced the mild stick with a wilder XR281HR.

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The new cam offered a 0.571/0.573 lift split, a 228/230 duration split at 0.050, and a 112-degree lobe separation angle (LSA). In one fell swoop, the cam swap increased both lift and duration while tightening the LSA. The result of the cam swap in our 5.3L was immediate and impressive, with the peak power output jumping to 480 hp. Peak torque was up by just 1 lb-ft, but the cam swap netted power gains from 4,700 rpm on up, with a loss in torque below that point. That’s the tradeoff.

Typical of a more aggressive cam profile, the idle vacuum dropped by over 3 inches, but Modern Mouse now sounded like one serious small-block, especially at full song. We’d love to stab this thing in a Camaro or Chevelle and start grabbing gears at 7,000 rpm! If that doesn’t bring a smile to your face, you must be a closet Ford owner.

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Though our cam swap netted some impressive numbers, we decided to keep going with a set of roller rockers and synthetic oil. Unfortunately for us, both changes were made at the same time, so you can judge for yourself just how much each might be worth. We can say they are both worthwhile upgrades and every motor deserves synthetic oil.

After the oil change to Luca 5W-20 synthetic, we also swapped out the stock rockers for a set of 1.8-ratio rollers from Comp Cams. The revised rocker ratio pushed the lift of our new XR281HR cam over 0.600 lift, but our spring package from Total Engine Airflow was more than adequate to handle the extra lift. A quick check on piston-to-valve indicated we didnít have much more room for additional duration, but the combination was ready to rock. The two changes improved the power output of the 5.3L to 492 hp and 447 lb-ft of torque. The additional rocker ratio improved power across the board.

The final test of the day involved nitrous oxide. NOS supplied a kit (part number 05169NOS) designed specifically for the LS2 (larger throttle body; it also has one for the LS1). The wet EFI kit included everything needed to increase the power output of the motor by as much as 200 hp. We chose slightly more conservative jetting to supply an additional 125 hp. We also added a can of octane booster to the premium unleaded (91 octane) pump gas we had been using for all of the testing. Using the Fast XFI management system, we also dialed out four degrees of timing to minimize the chance of detonation (remember those cast pistons). Westech had a bottle heater on hand to ensure over 900 psi of bottle pressure.

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Given the high-mileage short-block, we were a little nervous before hitting the button, but Modern Mouse responded like a real trooper. After minor changes to the air/fuel mixture (factory jetting from NOS is a tad on the rich side for safety), the 5.3L belted out 616 hp and 586 lb-ft of torque on the juice. That’s enough power to push a street machine into the 10s, trapping more than a few Mustangs in the process.

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16. As luck would have it, Modern Mouse was equipped with the very same heads, cam, and intake manifold as a 4.8L run for our sister book Hot Rod. The comparison is interesting, as the smaller 4.8L made peak power higher in the rev range and the larger 5.3L offered more average power through the entire rev range. Identically equipped, bigger really is better.

Power Numbers:

Base

281 Cam

Rkrs&Oil

NOS

RPM

HP TQ

HP TQ

HP TQ

HP TQ

2,600

N/A N/A

N/A N/A

N/A N/A

N/A N/A

2,900

204 369

N/A N/A

N/A N/A

N/A N/A

3,200

232 381

224 369

229 376

228 374

3,500

263 395

250 375

255 383

256 384

3,800

297 410

285 394

295 407

294 406

4,100

337 432

318 407

328 421

364 466

4,400

361 431

354 423

365 436

488 582

4,700

387 432

388 434

399 446

524 586

5,000

413 434

412 433

425 446

547 575

5,300

436 432

439 435

451 447

574 569

5,600

444 416

460 431

473 444

600 563

5,900

445 396

472 420

486 432

608 541

6,300

439 366

479 399

493 411

616 514

6,600

N/A N/A

480 382

492 391

521 415

Max

445 434

480 435

492 447

616 586

Effect of Displacement: 4.8L vs. 5.3L

The graph illustrates the difference in power production offered by the 4.8L and 5.3L. Both motors were equipped with stock short blocks, sporting the same XR281HR cam, TEA CNC-ported stock heads and Fast LSXR intake. Both combinations were also equipped with the very same 1-3/4-inch long-tube headers, Fast XFI management system, and Meziere electric water pump. The 4.8L produces 449 hp and 378 lb-ft of torque to the 480 hp and 435 lb-ft of torque offered by the larger 5.3L. It is also important to note that the smaller 4.8l produced peak power at 7,000 rpm and peak torque at 5,800 rpm. This compares to 6,600 rpm and 5,300 rpm for the larger 5.3L. Displacement has a way of taming the cam profile. Were we to run this combination on a 6.0L or a 408 stroker, the motor would make peak power even lower than the 5.3L. The 4.8L was no slouch, but just check out how much extra average power is available in the lower rev ranges. There really is no replacement for displacement.

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5.3L LS Small Block Build - LS Modern Mouse: Part 2

10 The XR281HR cam proved its worth by bumping the power output up to 480 hp and 435 lb-ft of torque. As expected, there was a trade off in low-speed power compared to the milder XR265HR cam, but the wilder cam improved the power output by over 40 hp.

Though we tested a new cam, rockers, and an NOS nitrous kit in this episode of Modern Mouse, we decided to give our readers a sneak peak at what we have planned for future installments. Modern Mouse will be subjected to strokers, intakes, and even boost.

1. The 5.3L short block was still sporting all of the factory internals. Donít be too quick to discount the strength of the factory stuff; our sister book Hot Rod ran some testing on a stock 4.8L short block and managed to exceed 1,200 hp using a pair of turbos.

2. Back in part one, we upgraded the stock heads by shipping them off to Total Engine Airflow for some CNC port work. The Stage 2 upgrade included valves, springs, and extensive porting. The heads were capable of supporting 600 hp.

3. The stock truck intake was ditched in favor of the Fast LSXR and matching 102mm throttle body. Possibly a tad oversized for the mild 5.3L, the head and intake combination were just begging for a wilder cam profile.

4. All testing was performed with a set of 1-3/4-inch long-tube headers feeding 18-inch collector extensions.

5. The stock 5.3L cam was replaced by a mild XR265HR grind from Comp Cams. The XR265HR cam offered 0.522/0.529 lift split, a 212/218 duration split, and a 14-degree lobe separation angle. The mild street cam offered impressive power gains through the entire rev range, but we knew there was more power to be had.

6. Before swapping the cam, we decided to upgrade the oiling system with a Moroso pan, pick-up, and windage tray. Designed for an F-body application, the combination is often used when swapping an LS into a early chassis.

7. Equipped with the 265 cam, TEA heads, and FAST intake in part one, Modern Mouse produced peak numbers of 445 hp and 434 lb-ft of torque. That became the baseline numbers for part two.

8. With plenty of head and intake flow, the 5.3L was just begging for more cam timing. The XR281HR cam from Comp Cams fit the bill perfectly by offering a 0.571/0.573 lift split, a 228/230 duration split, and a slightly tighter 112-degree lobe separation angle.

9. Out came the XR265HR cam and in went the wilder XR281HR grind. Cam swaps on an LS motor are a breeze compared to a conventional small-block. Rotating the cam pushes the lifters up into the plastic guides so it was unnecessary to remove the intake or cylinder heads to perform the cam swap.

10. The XR281HR cam proved its worth by bumping the power output up to 480 hp and 435 lb-ft of torque. As expected, there was a trade off in low-speed power compared to the milder XR265HR cam, but the wilder cam improved the power output by over 40 hp.

11.After swapping the cam we decided to change the oil. Originally we wanted to test the change to the lighter oil individually but a snafu in testing combined the oil and rocker swap. We filled the crankcase with Lucas 5W-20 synthetic then installed a new K&N oil filter.

12. Though equipped from the factory with partial roller rockers (trunion only), these full roller rockers from Comp Cams offer roller tips and trunions to further reduce friction. The 1.8:1 Comp roller rockers also increased the valve lift to over 0.600 lift. Luckily our TEA heads came with valvesprings that would accept the higher lift and offer the required valve control. The rockers and lightweight oil increased the power output of the 5.3L to 494 hp and 447 lb-ft of torque.

13. The final modification for Modern Mouse was nitrous oxide. In preparation of the significant boost in power, we added a can of Lucas Oil octane booster to the 91-octane, premium unleaded pump gas.

14. NOS supplied a nitrous kit designed specifically for the LS application. Since we were using the FAST intake and throttle body, we chose the system designed for the larger LS2 throttle body. The wet EFI kit was adjustable up to 200 hp, but we opted to run a 125hp shot on the modified 5.3L.

15. The NOS kit featured this trick throttle body sandwich plate that housed the fuel and nitrous fogger nozzles. With jetting to provide an additional 125 hp and our bottle heated to provide just over 900 psi of pressure, the NOS kit performed perfectly and power jumped to 616 hp and 586 lb-ft of torque. For additional safety, the FAST XFI management system was used to retard the timing by 4 degrees.

16. As luck would have it, Modern Mouse was equipped with the very same heads, cam, and intake manifold as a 4.8L run for our sister book Hot Rod. The comparison is interesting, as the smaller 4.8L made peak power higher in the rev range and the larger 5.3L offered more average power through the entire rev range. Identically equipped, bigger really is better.